Metal shapes having increased compressive strengths



June 28, 1966 R. P. LEVEY, JR 3,257,688

METAL SHAPES HAVING INCREASED COMPRESSIVE STRENGTHS Filed May 22, 1964 3 Sheets-Sheet 1 lll w '7 Hi Fig. 1

INVENTOR. Ralph P. Levey, Jr.

ATTORNEY.

June 28, 1966 R. P. LEVEY, JR

INVENTOR Ralph P. Levey, Jr.

RECONTOUR IN INCHES x10 f TTTTTTT Y.

June 28, 1966 R. P. LEVEY, JR

METAL SHAPES HAVING INCREASED COMPRESSIVE STRENGTHS Filed May 2?, 1964 3 Sheets-Sheet 3 I ELASTIC LlMlT NORlMAL WEDGE STRAIN, lN/lN x igl 7.

e STRAlN, IN/lN X 10 INVENTOK Ralph P. Levey, Jr.

ATTORNEY.

United States Patent 3,257,688 METAL SHAPES HAVING INCREASED COMPRESSIVE STRENGTHS Ralph P. Levey, .lra, Oak Ridge, Tenn., assignor to the United States of America as represented by the United States Atomic Energy Commission Filed May 22, 1964, Ser. No. 369,643 4 Claims. (Cl. 1816.5)

This invention relates generally to ultra-high pressure intensifiers and more particularly to a method of increasing the compressive yield strengths of components used therein.

A problem which has been characteristic of ultra-high pressure intensifiers is that of attaining ultra-high pressures without exceeding the compressive strength of components used therein. This problem is especially serious in those innermost portions of the intensifiers known as anvils, which are exposed to the ultra-high pressures developed in the pressure chamber. The remaining portions of the intensifier generally operate at much lower stress levels due to the geometric attenuation provided by their radially expanding cross sections.

A further problem has been the premature contacting of anvil members caused by the outward bulging of their contiguous side portions under load. When such contact occurs, there is a decrease in the pressure transmitted to the central pressure chamber and a resultant loss of etficiency by the intensifiers.

One partial, and perhaps obvious solution to this problem, is to fabricate of high strength materials those components of the intensifier which operate at high stress levels. However, since the highest strength materials which are presently available are already being used, further progress using this approach is limited by the rate at which higher strength materials are developed.

It is, accordingly, an object of the invention to provide means for increasing the compressive yield strengths of the presently available materials.

A further object of the invention is to provide means for preventing premature contact of anvil members during a pressing operation.

Other objects of the invention will become apparent from an examination of the following description of the invention and the appended drawings, wherein:

'FIG. 1 is a perspective view, partly cut-away, of an ultra-high pressure intensifier utilizing anvil members made in accordance with the present invention.

FIG. 2 is a full scale isometric view of an anvil member used in the intensifier of FIG. 1.

FIG. 3 is an isometric view of a frusto-conical type anvil made in accordance with the present invention.

FIG. 4 is an isometric view of a normal anvil test shape used in evaluating the subject invention.

FIG. 5 is a transverse section of the anvil test shape of FIG. 3 after it has been recontoured.

FIG. 6 is an isometric view of a simple right cylinder which was used to provide basic stress-strain data for evaluating the shapes of FIGS. 3 and 4.

FIG. 7 is a graph depicting the results of compressive strength tests of 30, normal and recontoured, anvils.

FIG. 8 is a graph depicting the results of compressive strength tests of normal and recontoured, anvils.

FIG. 9 is a graph of experimental data obtained for various values of recontour applied to a 45 steel anvil.

In accordance with the present invention, a method of increasing the compressive yield strengths of certain metal shapes such as the anvils used in ultrahigh pressure intensifiers, is provided. The subject method utilizes a recontouring of the metal shapes to provide slightly concave side faces. The recontours are generally circular arcs ter- 3,257,688 Patented June 28, 1966 minating slighty below the load surfaces of the metal shapes.

To facilitate an understanding of the invention reference is made to FIG. 1 wherein an ultra-high pressure intensifier known as the cubic intensifying array is shown in a perspective cut-away view. The cubic intensifier comprises a cylindrical housing 1 slidably containing therein six piston members 2 (two shown, two hidden, and two removed in FIG. 1), which are basically fr-usto-conical in shape. These pistons are equal in size and configuration. One piston is provided in each end of the cylindrical housing and four pistons are equally spaced around the sides thereof. The convergent end of each frustoconical piston 2 terminates as a cylindrical projection 3 whose outer :wall 4 mates in slidable relationship with a precisely machined nylon bushing 5 embedded in housing 1.

The divergent base of each piston 2 is further provided with a cylindrical axial projection 6 which terminates in a threaded portion. A piston retaining and aligning bar '7 is rigidly mounted on the outside of housing 1 perpendicular to the axis of piston 2.

concentrically mounted in the convergent base of pistons 2 are anvil members 8 comprising cylindrical bodies of tool steel tapered to square cross sections at their unmounted ends. The square end surfaces 9 of the anvil members form the sides of a cubical pressure chamber.

It is readily apparent that the stresses experienced by the tapered end portions of anvils 8 will be substantially greater than the stresses experienced elsewhere throughout the anvil and piston assembly. Applicants method of increasing the compressive yield strength of certain metal shapes is, accordingly, applied to the tapered end portions where yielding is most likely to occur.

FIG. 2 is a full size isometric view, partly exaggerated, of an anvil 8 of the intensifier of FIG. 1. As can be seen in FIG. 2, tapered portion 10 has been provided with a concave depression which terminates just short of load surface 9. The concave depression terminates just short of load surface 9 so as to enable the anvils 8 to more effectively seal the pressure chamber defined by the anvils, thereby minimizing leakage of pressure transmitting material. Tapered .portion 10 and the concave depression have been enlarged and highly exaggerated for clarity. Applicant has found that this concavity provides a 10 to 50 percent increase in compressive yield strength to otherwise conventional anvil members. The concave surface is generally provided by grinding away metal from the tapered surface along a circular arc.

Example An vil members similar to the anvil shown in FIG. 2 have been fabricated for use in the hereinbefore described cubic intensifying array. The anvil members were fabricated from a 3-inch nominal diameter cylindrical bar stock of AISI-M-lS grade tool steel. Load surface 9 is a 1 /3 inch square, and sloping surface 10 which intersects surface 9 at a degree angle has a slant height of 0.509 inch. A 60 inch radius contour is provided along surface 10 terminating approximately 0.08 to 0.10 inch from surface 9 and from second tapered portion 11 of anvils 8. The recontour reaches a maximum depth of 0.010 inch below the flat surface which existed prior to recontouring. Applicant conservatively estimates that at least a 10 percent increase in compressive yield strength will be provided by the recontouring of these anvils.

FIG. 3 illustrates a frusto-conical shaped anvil 16 made in accordance with the present invention. As can be seen from FIG. 3, the tapered side surface of the frustoconical end is provided with a concave depression 13, shown highly exaggerated, which terminates just short of load surface 14. Although anvil members which terminate in frusto-conical portions cannot be used in the cubic assembly illustrated herein, they are used in certain other in-tensifiers such as that disclosed in US. Patent No. 2,941,241.

FIGS. 4, 5 and 6 illustrate several simple test shapes used in a yielding study which provided information for the graphs of FIGS. 7, 8 and 9. A simple anvi-l shape as shown in FIG. 4 was supported on its larger surface 16 while pressure was applied to its smaller surface '17. The bulge h of side surfaces 18 was measured at yield and from this value a concave recontour, whose depth h substantially equaled the measured bulge, was machined into side surfaces 19 of recontoured anvil 20 shown in FIG. 5. Recontoured anvil 20 of FIG. 5 was supported and loaded in the same manner as anvil 15 of FIG. 4.

FIG. 6 illustrates a simple right cylinder 21 which provided stress-strain values for comparison with the stressstrain values of simple anvil shape 15 of FIG. 4 and recontoured anvil 20 of FIG. 5; thereby enabling the effect of the recontouring alone to be more readily determined.

An equation for determining the magnitude of anvil bulge for various sizes of anvil shapes and materials and for various pressures has been determined, and will provide approximate values enabling a recontour to be selected without the laborious and time consuming testing previously required. The equation is as follows:

where:

l=the slant height of the sloping side surface which is to be recontoured.

h=the amount of bulging which the sloping surface of a normal anvil will undergo at yield.

S=the arc length of the bulging side of a normal anvil at yield.

This equation may be solved for h and a value h of substantially the same magnitude selected. The symbols, h, S, and l are illustrated in FIG. 4 and the symbol h in FIG. 5. A chord length slightly less than the slant height I of the sloping side surface together with h determines a radius of curvature of the recontoured side surface 19 shown in the anvil of FIG. 5.

The results of several tests are shown in FIGS. 6 and 7 where strain as a function of stress for normal and recontoured anvil test shapes as illustrated in FIGS. 3 and 4 is shown. The ordinates of FIGS. 7 and 8 are given in fractions of the yield stress for a simple right cylindrical body as shown in FIG. 6. From FIG. 7, which is for normal and recontoured, wedges it is apparent that even the simple wedge shape provides an increase in the elastic limit over similar material in the form of a right cylinder. It can also be seen, however, that the recontoured 30 wedge provides a 16 percent increase in the elastic limit over the normal flat sided wedge. This may vary, of course, depending upon the particular size, shape and depth of recontour, and modulus of elasticity of the particular anvil being tested.

FIG. 8 is analogous to FIG. 7 except that a 45 wedge is tested with a resulting 27 percent increase in the elastic limit of the recontoured wedge over the normal flat sided wedge.

FIG. 9 illustrates the effect of various values of re contour on the yield strength of 45 steel anvils. The recontours, which terminated /8 inch from the load surface and base of the anvils, were circular arcs the maximum-depth of which is indicated along the abscissa of FIG. 9. The strengthening realized is shown along the ordinate. It can be seen from FIG. 9 that only a very small range of recontours provide any strengthening above the 1.5 strength factor provided by the unrecontoured shape alone, and that removal of an excess of material so as to provide a recontour of greater depth may actually prove deleterious to the yield strength of an anvil member. It is perhaps less apparent that recontours which fall within the range wherein only slight strengthening is provided may be economically unjustified. It is, therefore, important that recontours be provided as taught herein so as to strengthen rather than weaken the anvil member and to provide both the maximum strengthening and greatest economic justification. As pointed out hereinbefore, the depth of the recontour should be substantially equal in magnitude to the height of the bulging which the non-recontoured anvil member would have undergone at yield. The wedges of FIG. 9, for example, were calculated to reach a yield condition with their sides bulging about 0.006 inch. As can be seen from FIG. 9, a recontour of 0.006 inch depth would have provided a strengthening factor of about 2.4 which is near the peak value of 2.5. The 60 percent increase in yield strength indicated in FIG. 9 substantially exceeds the strengthening provided to the 45 wedges tested in FIG. 8. This higher value is attributed to the fact that two dimensional test shapes (cones and pyramids) were used rather than the one dimensional wedge shapes used in the graphs of FIGS. 7 and 8.

It is noted that FIG. 9 is not intended to teach any specific value of recontour depth for general use. The values of strengthening factor versus recontour will vary for various sizes and shapes of anvil members and for various anvil materials with different moduli of elasticity;

These factors are taken into consideration in the aforesaid equation for determining anvil bulge.

In addition to .the strengthening obtained with the recontoured anvil shapes, a second beneficial result was also realized. The recontoured anvils increased the intensifier efficiency by reducing deleterious contact between the bulging sides of the converging anvils. Although the anvils still bulge under pressure, they bulge less because of .the strengthening effect of the recontour, and they are less likely to contact because they have to bulge further than previously before contacting.

'Recontours other than circular arcs have also increased the strengths of test shapes. Circular recontours have been used primarily, however, as they are believed to approximate a normal-bulge contour, and are readily machined. Other arcuate recontours as Well as a V-shaped recontour provided by the intersection of two slightly inclined intersecting planor surfaces, also provided the benefits of the present invention in varying degrees to test shapes.

The above description of one form of the invention was offered for illustrative purposes only and should not be interpreted in a limiting sense. For example, the benefits of the present invention can be provided with varying effectiveness by providing recontours other than circular arcs. The present invention may also be applied to workpieces other than the illustrated anvil members such as hollow rings, truncated cones, right prisms and cylinders. Accordingly, it is intendedthat the invention be limited only by the claims appended hereto.

What is claimed is:

1. A method of increasing the compressive strength of an anvil member for use in an ultra-high pressure intensifier, comprising:

(a) determining the bulging of a tapered side surface of said anvil when said anvil is loaded to the yield point of said side surface, and

(b) recontouring said tapered side surface to form a concave depression therein having a depth substantially equal in magnitude to the height of said bulging.

2. An improved anvil member for use in an ultra-high pressure intensifier comprising a load surface, and a slant-' ing a concave depression immediately adjacent said first portion, the spacing h between an innermost surface of said depression and a projection of said first portion being determined essentially in accordance with the following equation:

and a third portion of uniform slope immediately adjacent said second portion, said third portion having the same slope as said first portion and coinciding with a projection from said first portion.

3. The improved anvil member of claim 2 wherein said load surface and said slanting side -wall define a truncated pyramid.

4. The improved anvil member of claim 2 wherein said load surface and slanting side wall define a truncated cone.

References Cited by the Examiner UNITED STATES PATENTS 2,941,248 6/ 1960 Hall. 3,075,245 1/1963 Bundy. 3,179,979 4/ 1965 Bundy et al.

WILLIAM J. STEPHENSON, Primary Examiner. 

1. A METHOD OF INCREASING THE COMPRESSIVE STRENGTH OF AN ANVIL MEMBER FOR USE IN ULTRA-HIGH PRESSURE INTENSIFIER, COMPRISING: (A) DETERMINING THE BULGING OF A TAPERED SIDE SURFACE OF SAID ANVIL WHEN SAID ANVIL IS LOADED TO THE YIELD POINT OF SAID SIDE SURFACE, AND (B) RECONTOURING SAID TAPERED SIDE SURFACE TO FORM A CONCAVE DEPRESSION THEREIN HAVING A DEPTH SUBSTANTIALLY EQUAL IN MAGNITUDE TO THE HEIGHT OF SAID BULGING. 